Preheat oven to 350. Prepare two 9x5x3" loaf pans by spraying pans with cooking spray, then lining the length of the pans with a strip of parchment paper, and spraying the parchment.

Triple sift the flours, baking powder and salt into a medium bowl and set aside.

Combine the buttermilk and lemon juice and set aside.

Beat butter on high speed for 1 minute until soft and creamy. Slowly add sugar and lemon zest, and beat on high for 10 minutes, until white, light and fluffy. Scrape sides of bowl with a rubber spatula.

Add eggs, one at a time, incorporating each thoroughly.

Add 1/3 of the sifted dry ingredients, and mix on low speed. Add 1/3 of buttermilk mixture and beat until incorporated. Repeat with remaining 2/3 in two additions.

Make syrup by boiling lemon juice and sugar for about 2-3 minutes, stirring, until sugar is dissolved. Poke holes in cakes with a skewer, and using a pastry brush, brush on 2-3 coats of syrup over warm cake.